<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>03_流程控制</title>
</head>
<body>
<script>
    //1.顺序结构
    console.log('1');
    console.log('2');
    console.log('3');
    //2.分支结构
    let username = '';
    //若用户名是空串''转为布尔是false，!false为true，会走分支1
    if (!username){
        alert('用户名不能为空！');
    }else {
        alert('欢迎'+username+'回归！');
    }
    //3.选择分支
    let gender = 6;
    switch (gender){
        case 1:
            console.log('男');
            break;
        case 0:
            console.log('女');
            break;
        default:
            console.log('未知');
    }
    //4.循环结构
    let names = ['张三','李四','王五','赵六','钱七'];
    for (let i = 0; i < names.length; i++) {
        console.log(names[i]);
    }
    //如果用var定义循环变量i，循环结束后在此处仍能打印出i的值
    //但如果用let定义，就会报错：变量i不存在！
    console.log(i);

    //增强for循环
    //let name 表示遍历names数组时,本轮遍历到值
    for(let name of names){
        console.log(name);
    }


</script>
</body>
</html>